Use of Psinsar™ Data to Infer Active Tectonics: Clues on the Differential Uplift Across the Giudicarie Belt (Central-Eastern Alps, Italy)
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Tectonophysics 476 (2009) 297–303 Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto Use of PSInSAR™ data to infer active tectonics: Clues on the differential uplift across the Giudicarie belt (Central-Eastern Alps, Italy) M. Massironi a,⁎, D. Zampieri a, M. Bianchi b, A. Schiavo c, A. Franceschini d a Dipartimento di Geoscienze dell'Università di Padova, Via Giotto 1, 35137 Padova, Italy b Tele-Rilevamento Europa - T.R.E. s.r.l., Via Vittoria Colonna, 7, 20149 Milano, Italy c Land Technology and Services s.r.l., Via Sartorio, 12, 31100 Treviso, Italy d Servizio Geologico della Provincia Autonoma di Trento, Via Roma 50, 38100 Trento, Italy article info abstract Article history: The Permanent Scatterers Synthetic Aperture Radar INterferometry (PSInSAR™) methodology provides high- Received 21 December 2007 resolution assessment of surface deformations (precision ranging from 0.8 to 0.1 mm/year) over long periods Accepted 28 May 2009 of observation. Hence, it is particularly suitable to analyze surface motion over wide regions associated to a Available online 6 June 2009 weak tectonic activity. For this reason we have adopted the PSInSAR technique to study regional movement across the Giudicarie belt, a NNE-trending trust belt oblique to the Southern Alpine chain and presently Keywords: characterized by a low to moderate seismicity. Over 11,000 PS velocities along the satellite Line Of Sight (LOS) PSInSAR were calculated using images acquired in descending orbit during the 1992–1996 time span. The PSInSAR Active tectonics – Giudicarie belt data show a differential uplift of around 1.4 1.7 mm/year across the most external WNW-dipping thrusts of the Giudicarie belt (Mt. Baldo, Mt. Stivo and Mt. Grattacul thrusts alignment). This corresponds to a horizontal contraction across the external part of the Giudicarie belt of about 1.3–1.5 mm/year. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Radar INterferometry (PSInSAR™)(Ferretti et al., 2000, 2001; Colesanti et al., 2003), allows the identification and use, during the interferometric Since the 1993 work of Massonet et al. dealing with the co-seismic process, of radar phase stable points normally corresponding to buildings ground movements related to the Landers earthquake (California, 28 or single outcrops (i.e. permanent scatterers). This strongly minimizes June 1992, Mw 7.3; e.g. Kanamori et al., 1992; Sieh et al., 1993), the phase dispersions and the consequent loss of coherence between time remote sensing Synthetic Aperture Radar INterferometry (InSAR) has delayed acquisitions. Hence, although this method does not give regional been extensively used for active deformation assessment. InSAR uniformly distributed information on surface movements as the classic provides a one-dimensional measurement of change in distance InSAR procedure, it is particularly suitable for high-resolution assess- between the surface and the spacecraft along the Line Of Sight (LOS or ment of surface deformations (precision up to 0.1 mm/year) to be slant-range) of the Synthetic Aperture Radar (SAR) sensor. In the field of realized over a long period of observation using a great amount of SAR fault tectonics InSAR processing has been extensively applied to record images. For these reasons PSInSAR has recently proved to be very co-seismic (e.g. Zebker et al., 1994; Massonet et al., 1994; Tobita et al., effective in resolving surface motion of seismic areas during inter-seismic 1998; Pedersen et al., 2003; Wang et al., 2006) and post-seismic (e.g. periods or even of wide regions presently involved by very low tectonic Peltzer et al., 1996; Atzori et al., 2008) signatures, derive focal movements (provided that a detection of a considerable amount of PS is mechanisms, fault geometry and in general source models (e.g. Feigl guaranteed) (Bürgmann et al., 2006; Vilardo et al., 2009). et al.,1995; Acoglu et al., 2006; Peyret et al., 2008; Sudhaus and Jonsson, In this work we have applied the PSInSAR method to obtain new 2009) and even evaluate inter-seismic strain (Cavaliè et al., 2008). insights into the present-day deformation pattern of the southern However, the major draw-back of the classical InSAR techniques, Giudicarie belt, which is a key sector of great tectonic complexity within which rely on a stack of several interferograms, is the possible lack of the post-collisional south-vergent thrust system of the Southern Alps coherence between the time delayed SAR couples acquired on vegetated (Italy) (Castellarin et al., 2006; Massironi et al., 2006; Viganò et al., 2008). and/or mountain areas and/or in different atmospheric conditions. A recent InSAR technique, the Permanent Scatterers Synthetic Aperture 2. The Giudicarie belt ⁎ Corresponding author. Fax: +39 049 8272010. 2.1. Geological setting E-mail addresses: [email protected] (M. Massironi), [email protected] (D. Zampieri), [email protected] (M. Bianchi), [email protected] (A. Schiavo), [email protected] The post-collisional south-vergent belt of the Southern Alps shows (A. Franceschini). its maximum complexity at the Giudicarie belt. NNE-trending system 0040-1951/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.tecto.2009.05.025 298 M. Massironi et al. / Tectonophysics 476 (2009) 297–303 Fig. 1. Structural sketch of the central and eastern Southern Alps. is oblique to the Southern Alps chain (Fig. 1) and results from tectonic worthy to be mentioned is the southern Mt. Baldo, an area where reactivation and inversion of an Early Jurassic extensional domain several historical earthquakes are reported (Boschi et al., 2000). The related to the continental rifting of the Adria margin (e.g., Bertotti et ridge of the Mt. Baldo is displaced by a 4.5-km-long normal fault, al., 1993). On the whole, the southern Giudicarie belt develops along which originated the narrow Naole valley parallel to the ridge. the transition between basinal (Lombardy basin) and platform Trenches excavated at the base of the fresh carbonate bedrock scarp (Venetian platform) domains (Trevisan, 1939; Castellarin, 1972), affecting the western slope of the Naole valley have shown an activity where many sub-basin depocentres have formed. These basins are of the fault between the Late Pleistocene and Holocene (subsequent to bounded by steep to middle angle synsedimentary faults, generally 17,435–16,385 BP, 14C cal. age, Galadini et al., 2001). A mixed dipping towards the west and E–W steep transfer faults (Castellarin gravitational-tectonic origin for this deformation has been suggested and Picotti, 1990). by Galadini et al. (2001) and Sauro and Zampieri (2001). The Giudicarie fault system exhibits a structural boundary also at crustal (Scarascia and Cassinis, 1997) and lithospheric (Lippitsch et al., 2.2. Seismotectonic setting 2003) scales. In its southern sector (south of the intersection with the Tonale The Giudicarie belt is characterized by low instrumental seismicity fault, Fig. 1) the Giudicarie fault separates the Tertiary Adamello (Slejko et al., 1989; Carulli and Slejko, 2009)withfewmoderate batholith and the Variscan basement to the west and northwest from earthquakes (Pondrelli et al., 2007), most of which are located in the the sedimentary cover of the Southern Alps with thin basement slices upper crust (Scarascia and Cassinis, 1997; Viganò et al., 2008). The most to the east. The South Giudicarie fault system is composed of WNW- important historical earthquakes (I0 IX MCS) for northern Italy occurred dipping steep to subvertical fault planes, which being oblique to the in 1117 in the Verona area and in 1222 near Brescia (Guidoboni, 1986; Alpine belt have accommodated transpression. Its Neogene kinematic Guidoboni and Comastri, 2005; Guidoboni et al., 2005; Stucchi et al., role is that of an oblique ramp of the S-vergent Val Trompia thrust to 2008), both located just at the southern end of the belt. Along the Adige which it is connected towards the south (Picotti et al., 1995)(Fig. 1). valley, the Roman archaeological site of Egna shows evidences of Slip partitioning has produced distributed sinistral strike-slip move- destruction related to an earthquake of similar intensity that happened ments on steep faults and dip-slip reverse movements on moderate in the mid 3rd century AD (Galadini and Galli,1999; Galadini et al., 2001; dipping N to NNE-trending faults within a wide belt comprised Stucchi et al., 2008). In addition, Quaternary faults have been recently between the Giudicarie and Adige valleys (Prosser, 1998; Viola et al., located within the epicentral area of the strong 1222 Brescia earthquake 2001; Massironi et al., 2006). (Sileo et al., 2007; Livio et al., 2009a,b). The study area has been affected by strong exogenic modelling The strongest recent events are the Mw 4.8 Merano earthquake, related to the Late Pleistocene glacial activity and post-glacial fluvial which occurred on 17 July 2001 close to the North Giudicarie Line erosion. Therefore, most geomorphic evidence of Quaternary tectonics (Caporali et al., 2005; Pondrelli et al., 2006) and the ML 5.3 Salò event, has been strongly modified and often completely erased, and the which struck the western coast of the Lake Garda on 24 November depositional units suitable for dating are quite rare. The only case 2004 (Baer et al., 2005; Pondrelli et al., 2006). M. Massironi et al. / Tectonophysics 476 (2009) 297–303 299 In the seismic source model for seismic hazard assessment (Meletti Satellite INterferometry of Synthetic Aperture Radar data (InSAR) is et al., 2008) this region has been included in a common zone where the based upon phase comparison of SAR images acquired at different times NW-trending strike-slip faults of the Schio-Vicenza fault system and and views (Curlander and McDonough,1991). The Permanent Scatterers the NNE-trending Giudicarie transpressional system interact. In fact, are high RADAR reflecting objects that do not change their spectral the distribution of the events which occurred during the last decades is response for different acquisitions (i.e.